1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine and a printer. More particularly, the invention relates to an image forming apparatus provided with discharge wires.
2. Related Background Art
Conventionally, for the image forming apparatus, such as an electronically photographic copying machine, which is provided with charging means using charging wires, it has been generally practiced to arrange cleaning means for removing stains caused by the repeated used of the charging wires. The cleaning means is structured in such a manner that each of the cleaning pads or the like is allowed to slide on the tensioned charging wire so that the stains adhering to the charging wire are removed by the periodic operation of cleaning means.
As the charging wire, a tungsten wire is used. There are also used a gold-plated wire which is the tungsten wire plated with gold on its surface, and an oxidized tungsten wire which is the tungsten wire processed by oxidation.
Also, as the cleaning pads, there are used various ones in the range from the pad having an abrasive force weak enough so as not to peel off the gold plate to the pads having the reinforced abrasive force in combination with the tungsten wire.
However, with the adoption of the conventional art, the following drawbacks are encountered: At first, for use of the gold-plated wire, it is usually practiced to adopt its combination with pads having the weaker abrasive force so as not to cause the gold plate to be peeled off. Therefore, although it is possible to execute charging uniformly without any unevenness in the earlier stage following the replacement of such pads, the uneven images are produced eventually when stains are caused by the repeated use of the charging wires, because the pads having the weaker abrasive force cannot remove stains sufficiently.
Then, when the tungsten wires, and the pads each having a strong abrasive force are combined, the stains that may take place by the repeated use of the charging wires can be removed by the application of such strong abrasive force of each pad. However, since the tungsten wires tend to be naturally oxidized, the uneven images are formed after all in the earlier stage after the pads have been replaced if the tungsten wires which have been naturally oxidized should be used. Further, with the usual abrasion, the oxidized portions of the wires cannot be removed, and it is made impossible to recover such image unevenness. Here, however, after discharging is continued by the repeated use, the wires are oxidized entirely, then, it becomes possible to recover the image unevenness gradually.
Also, when the oxidized tungsten wires and the pads having strong abrasion force are combined for use, the stains that take place by the repeated use of the charging wire can be removed by such abrasive force of each pad, and no image unevenness may result unless cleaning is conducted in the earlier stage after the pads have been replaced. Nevertheless, if the wire cleaning is once conducted, the oxidized film is peeled off, and the film thus peeled off may adhere to the wire to cause uneven discharging, which results in the image unevenness after all.